JP2002292245A - Denitration catalyst and dioxin decomposing catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a denitration catalyst or dioxin decomposing catalyst having high catalytic activity even when SO2 and NH3 are present in low temperature exhaust gas. SOLUTION: The denitration catalyst contains TiO2 , BPO4 and WO3 . The dioxin decomposing catalyst contains TiO2 , BPO4 and WO3 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration catalyst and a dioxin decomposition catalyst having high catalytic activity even in low-temperature exhaust gas.

[0002]

2. Description of the Related Art In a refuse incinerator, a denitration catalyst or a dioxin decomposition catalyst is used to remove nitrogen oxides and dioxin from exhaust gas. Here, the denitration catalyst is a catalyst having an action of reducing NO _x in exhaust gas to N ₂ under the supply of NH ₃ , and is generally TiO ₂ , WO ₃
And a catalyst comprising V ₂ O ₅ . The catalyst generally exhibits high catalytic activity under high temperature conditions exceeding 300 ° C., and is also used as a dioxin decomposition catalyst because it can oxidatively decompose dioxins.

When the above catalyst is used as a denitration catalyst or a dioxin decomposition catalyst, the catalyst is usually used for treating exhaust gas at a relatively low temperature after dust and the like are removed through a dust filter or the like. For this reason, the use temperature of the catalyst is relatively low, for example, 300 ° C. or less, and the catalyst activity is often low. As a method of increasing the denitration rate or dioxin decomposition rate under such low-temperature conditions, generally, a large amount of V ₂ O ₅ having high low-temperature activity is added to the catalyst.

[0004]

However, garbage burning
SO is contained in the exhaust gas from_TwoIs often included
No. Under such conditions, the above catalyst is used as a denitration catalyst.
Then, SO in exhaust gas_TwoIs V in the catalyst_TwoO_FiveOxidized by
SO_ThreeAnd the SO_ThreeSupplied with NH _ThreeWhen
React (NH_Four)_TwoSO_ThreeEtc.
This is TiO_Two-WO _Three-V_TwoO_FiveDeposited on the surface of the catalyst
Significantly reduces catalyst activity. Therefore, S in the exhaust gas
O_TwoIf the concentration is high, V_TwoO_FiveCan not carry much
From the above, the catalyst activity of the catalyst can not be sufficiently high or
Even if the catalyst performance is improved, acidic ammonium sulfate is
There is a problem that the catalyst is deteriorated due to clogging.

Accordingly, an object of the present invention is to provide a denitration catalyst or a dioxin decomposition catalyst having high catalytic activity even at a low temperature of 300 ° C. or lower exhaust gas.

[0006]

Under such circumstances, the present inventors have conducted intensive studies and as a result, have found that conventional TiO ₂ -WO
_{It has been found} that when BPO ₄ is blended in a _3- V ₂ O ₅ catalyst, high catalytic activity can be maintained even under conditions where SO ₂ and NH ₃ are present in low-temperature exhaust gas, and the present invention has been completed. .

That is, the present invention relates to TiO ₂ , BPO ₄
And a denitration catalyst characterized by containing WO ₃ .

Further, the present invention provides a dioxin decomposition catalyst comprising TiO ₂ , BPO ₄ and WO ₃ .

[0009]

DETAILED DESCRIPTION OF THE INVENTION The denitration catalyst according to the present invention is made of TiO.
₂ , BPO ₄ and WO ₃ . The denitration catalyst according to the present invention may be composed of only three components of TiO ₂ , BPO ₄ and WO ₃ , but may further contain other catalyst components as long as the catalyst is not poisonous to the above catalyst. Such other catalyst components include, for example, V ₂
O ₅ , Cr ₂ O ₃ , Fe ₂ O _{3 and the} like can be mentioned.

[0010] As TiO ₂ used in the present invention, rutile, anatase, may be mentioned any of brookite, of anatase, operating temperature 20 ° C. to 500 ° C.
Within the range, the specific surface area is highest and the catalytic activity is high, so that it is preferable. WO ₃ and BPO ₄ are not particularly limited, and ordinary ones can be used.

In the denitration catalyst according to the present invention, one component of the catalyst component is
BPO as a minute_FourIs used. BPO_FourIs usually used
V_TwoO_FiveOxidizing power is lower than that of SO_Twoas well as
NH _ThreeUsed as a catalyst component in low-temperature exhaust gas containing
Even SO_TwoIs SO_ThreeIs hardly oxidized to
The catalyst can be kept highly active because it hardly occurs. Also, BPO
_FourIs a pole of cristobalite type structure consisting only of nonmetallic elements
It is hard to volatilize and is almost volatile up to 1450 ° C
It does not emit and is a stronger solid acid. Like this, BPO_Four
Is composed of only non-metallic elements and is usually used as a catalyst component
SO unlike metal oxide_TwoSulfidation even when in contact with
Hard to do. Also BPO_FourIs a solid acid, so SO_TwoTo
High durability.

The denitration catalyst according to the present invention contains TiO _{2 in an amount} of usually ₂₀ to 99.9% by weight, preferably 40 to 90% by weight. If the content of TiO ₂ is less than 20% by weight, it cannot function as a catalyst carrier, which is not preferable.

The denitration catalyst according to the present invention contains BPO _{4 in an amount} of usually 0.1 to 20% by weight, preferably 0.5 to 10% by weight. BPO ₄ is undesirable because is not expressed catalytic effect that it is less than 0.1 wt%. Further, BPO ₄ is not improved any more catalytic performance exceeds 20 wt% is not preferred because the relatively WO ₃ is less hot activity decreases.

In the denitration catalyst according to the present invention, WO ₃
-80% by weight, preferably 5-30% by weight. WO ₃
If it is less than 2% by weight, the catalytic performance at high temperatures is undesirably reduced. On the other hand, if WO ₃ exceeds 80% by weight, the catalytic performance will not be further improved and the cost will be undesirably high.

Further, the denitration catalyst according to the present invention further comprises V
_When it is a four-component composition containing ₂ O ₅ in a specific amount or less,
This is preferable because the low-temperature activity becomes high. The denitration catalyst according to the present invention contains V ₂ O ₅ usually at most 5% by weight, preferably at most 3% by weight. In the denitration catalyst according to the present invention, V ₂ O ₅
When the supported amount of is increased, the low-temperature activity of the catalyst is improved. However, when V ₂ O ₅ exceeds 5% by weight, SO _{3 of} SO ₂
This is not preferable because the conversion rate to sulfur becomes high and acidic ammonium sulfate is generated, causing clogging of the catalyst.

The denitration catalyst according to the present invention is, for example, a catalyst-supporting honeycomb body in which a denitration catalyst is supported on a paper corrugated honeycomb, or a pellet obtained by molding and firing a denitration catalyst together with a sintering aid, or extrusion molding formed by extrusion and firing. Used as a honeycomb body.

When the denitration catalyst is a carrier-supported honeycomb body, the denitration catalyst according to the present invention is supported on a honeycomb carrier. As the honeycomb carrier used in the present invention, a paper corrugated honeycomb in which flat fiber paper and corrugated fiber paper are alternately laminated and bonded is preferable because it is lightweight and can increase the catalyst carrying area. Examples of the material of the flat fiber paper and the corrugated fiber paper include non-woven fabrics and woven fabrics such as ceramic fibers, glass fibers, alumina fibers, mullite fibers, rock wool, and so-called biosoluble fibers. When the denitration catalyst is a pellet and an extruded honeycomb body, the pellet and the extruded honeycomb body may be formed by appropriately blending a firing aid with the denitration catalyst.

Next, a method for producing the denitration catalyst according to the present invention will be described. First, when the denitration catalyst according to the present invention is a carrier-supporting honeycomb body, it can be produced, for example, by the following production method. First, TiO ₂ , BPO ₄ and WO
₃ or a solution or slurry in which V ₂ O ₅ is further supported, if necessary, is prepared. The raw material of TiO ₂ used for preparing the solution includes titanium oxyhydroxide, titania sol, titanium oxide and the like. Examples of the raw material for BPO ₄ include boric acid as a boron source and diammonium hydrogen orthophosphate and phosphoric acid as a phosphorus source. Examples of these combinations include boric acid and diammonium hydrogen orthophosphate, and boric acid and phosphoric acid. WO ₃
Examples of the raw material include ammonium tungstate. Examples of the raw material for V ₂ O ₅ include vanadyl oxalate and ammonium vanadate.

The concentration of Ti in the solution or slurry is usually 20 to 70% by weight, preferably 30 to 60% by weight in terms of TiO ₂ . The concentration of B, P, W, V, etc. in the solution or slurry is as follows:
The proportion of the supported amount of TiO ₂ , BPO ₄ , WO _3, V ₂ O _5, etc. in the obtained catalyst is appropriately adjusted so as to be within the above range.

Next, after the carrier is immersed in each of the above solutions or slurries, the carrier is pulled up, evaporated to dryness, and fired. The firing temperature varies depending on the type of the immersed solution, but is usually 400 to 600 ° C., preferably 450 ° C.
５550 ° C. When the firing temperature is less than 400 ° C,
It is not preferable because the catalyst component is not sufficiently oxidized, and the heat during the use of the catalyst tends to increase the particle size of the catalyst and decrease the specific surface area of the catalyst. On the other hand, if the calcination temperature exceeds 600 ° C., the specific surface area of the catalyst decreases, and the activity decreases, which is not preferable. The firing time is usually 30
Minutes to 5 hours, preferably 1 to 3 hours. The above-described immersion, drying, and calcination steps are performed for each solution or slurry of the catalyst components, and all the catalyst components are supported on a carrier, whereby the denitration catalyst according to the present invention is obtained.

When the denitration catalyst according to the present invention is a pellet or an extruded honeycomb body, the ratio of the supported amount of TiO ₂ , BPO ₄ , WO ₃ and V ₂ O ₅ in the obtained catalyst is within the above range. It may be appropriately adjusted so as to fall within the range, and may be manufactured by a conventional method.

The denitration catalyst according to the present invention uses NH _{3 in the} exhaust gas.
And can be used as a denitration catalyst for reducing NO _x to N ₂ . Further, the above denitration catalyst can also be used as a dioxin decomposition catalyst.

The denitration catalyst according to the present invention can be used as a denitration catalyst for exhaust gas and the like used in refuse incinerators and the like, and the dioxin decomposition catalyst according to the present invention can be used as a dioxin decomposition catalyst for exhaust gas and the like used in refuse incinerators and the like.

[0024]

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 Ceramic fiber (trade name: Fineflex; Nichias)
100 parts by weight (made by Co., Ltd.) and polyvinyl chloride as binder
From 2 parts by weight of alcohol and water, ceramic fiber and
Slurry with a total amount of polyvinyl alcohol of 1% by weight
Was prepared. Next, the slurry is subjected to a conventional method using a circular mesh machine.
Paper having a porosity between fibers of 90% and a thickness of 0.3 mm.
A flat ceramic paper was obtained. This flat sera
Mick paper with or without corrugation
And for corrugating, a pair of upper and lower
Corrugated ceramic paper
And par. This corrugated ceramic paper
90 parts by weight of Royal silica and 10 parts by weight of Aerosil
Apply the mixed paste and mix with the flat ceramic paper.
Pressure and glue, corrugated ceramic paper and flat plate
Honeycomb basic structure integrated with ceramic paper
Formed body. The basic structure of the honeycomb
Was cut to a length of 500 mm. Next, Hanika
On the peak of the corrugated ceramic paper of the base structure
Glue is applied, and the other honeycomb basic structure
Laminating work with a ceramic paper side of 2 height
Perform until the thickness reaches 50mm, dry, and measure the length in the ventilation direction.
Is cut to 1000mm, frontage 500mm x height
Obtain a honeycomb structure of 250 mm in length x 1000 mm in depth
Was. This honeycomb structure of corrugated ceramic paper
The bitch was 7.5 mm and the cell height was 3.7 mm. Get
The honeycomb structure thus obtained is made of 30% by weight of colloidal silica in water.
Impregnated with the solution, dried and fired at 500 ° C for 2 hours
The hardened structure was subjected to a hardening treatment. Next, this honeycomb structure
The body was immersed in a 30% by weight aqueous solution of titanium oxyhydroxide.
After that, it is dried and calcined at 500 ° C for 2 hours to carry titania.
did. Furthermore, this honeycomb structure is
Water solution of 10.0% by weight of monium and 4.7% by weight of boric acid
After being immersed in the solution, it is dried and baked at 350 ° C. for 1 hour.
PO_FourWas carried. Furthermore, this honeycomb structure is meta-
Ammonium tungstate aqueous solution (tungsten oxide
85g / l) and vanadyl oxalate aqueous solution
(With a concentration of 3 g / l in terms of vanadium oxide)
After drying, baking at 500 ° C for 2 hours
_ThreeAnd V_TwoO_FiveWas obtained. C
The honeycomb supported catalyst is TiO_TwoThe loading amount is 90 g / l, and
, Composition weight ratio TiO _Two: BPO_Four: WO_Three: V_TwoO_Five
Was 83.6: 8.6: 6.6: 1.2. Obtained
NO catalyst, NO decomposition rate and pseudo dioxin
The decomposition rates of all chlorobenzenes were measured. The measurement is as follows
I went as follows. Figure 1 shows the results of the NO decomposition rate.
Table 1 shows the results of the benzene decomposition rate. -Measuring method of NO decomposition rate: (passing gas conditions) SV: 10000 / hr NO: 200 ppm O_Two : 7% H_TwoO: 5% SO_Two : 5 ppm NO / NH_Four : 1.0 ・ Measurement method of chlorobenzene decomposition rate: (gas flow conditions) SV: 1000 / hr Chlorobenzene: 0.2ppm O_Two : 12% N_Two : 73% H_TwoO: 15% Air: 2.43 l_N/ min^{* 1}(N_Two79%, O_Two21%) Nitrogen: 1.82 l_N/ min^{* 1} Pure water: 0.75 l_N/ min^{* 1}(0.60 ml / min in terms of liquid) Total: 5.00 l_N/ min^{* 1} * 1 "l_N"Indicates a gas amount converted to a standard state.

[0026]

[Table 1]

COMPARATIVE EXAMPLE 1 A honeycomb structure was treated with diammonium hydrogen phosphate at 10.0 weights.
% And an aqueous solution containing 4.7% by weight of boric acid, and then dried.
Baked at 350 ° C for 1 hour_FourOperation carrying
Was performed in the same manner as in Example 1 except that
A supported catalyst was obtained. The honeycomb supported catalyst is TiO_TwoCarry amount
Is 90 g / l and the composition weight ratio is TiO. _Two: WO_Three: V
_TwoO_FiveWas 91.5: 7.2: 1.3. Got
For the catalyst, the NO decomposition rate and chloro
The benzene decomposition rate was measured. The results are shown in FIG. 1 and Table 1.
You.

As is clear from FIG. 1, TiO ₂ -BP
The catalyst according to Example 1 supporting O ₄ -WO ₃ -V ₂ O ₅ is Comparative Example 1 consisting of only TiO ₂ -WO ₃ -V ₂ O _5.
Denitration rate at a low temperature of 300 ° C. or less than the catalyst according to
It is as high as 0%. Further, as is clear from Table 1, the catalyst according to Example 1 was 250 times less than the catalyst according to Comparative Example 1.
The decomposition rate of chlorobenzene at a low temperature of not more than 2 ° C is more than twice as high.

[0029]

The denitration catalyst and dioxin decomposition catalyst according to the present invention contain TiO ₂ , BPO ₄ and WO ₃ , and therefore have a high denitration rate at a low temperature of 300 ° C. or less.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between catalyst temperature and NO decomposition rate.

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Claims (6)

[Claims] 1. A denitration catalyst comprising TiO ₂ , BPO ₄ and WO ₃ . 2. The denitration catalyst according to claim 1, further comprising V ₂ O ₅ in an amount of 5% by weight or less. 3. 20-99.9% by weight of TiO ₂ , BPO
₄ 0.1-20% by weight, WO ₃ 2-80% by weight and V ₂
3. The denitration catalyst according to claim 1, comprising 5% by weight or less of O ₅ . 4. A dioxin decomposition catalyst comprising TiO ₂ , BPO ₄ and WO ₃ . 5. The dioxin decomposition catalyst according to claim 4, further comprising V ₂ O ₅ in an amount of 5% by weight or less. 6. TiO _{2 20 to} 99.9% by weight, BPO
₄ 0.1-20% by weight, WO ₃ 2-80% by weight and V ₂
O 5 ₅ wt% claim 4 or 5, wherein the dioxin decomposition catalyst, characterized in that it comprises the following.